Fail closed on missing example goldens

Author: code5717

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Changed
+- Normal example verifier runs now fail closed when a golden output fixture is
+  missing; only explicit `--update-golden` runs write fixture files.
 - Documentation now scopes the low-recursion implementation claim to the
   compiler stages that are actually stack-based today and tracks fully
   iterative backend emission as follow-up work.

scripts/verify_examples_common.py

@@ -148,12 +148,16 @@ def verify_example(
     fixture_path = fixtures_dir / f"{example.stem}.out"
     result.output_path = str(fixture_path)
 
-    if update_golden or not fixture_path.exists():
+    if update_golden:
         fixture_path.parent.mkdir(parents=True, exist_ok=True)
         fixture_path.write_text(actual, encoding="utf-8")
         result.output_match = True
         return result
 
+    if not fixture_path.exists():
+        result.error = f"missing golden fixture: {fixture_path}"
+        return result
+
     expected = fixture_path.read_text(encoding="utf-8")
     if actual == expected:
         result.output_match = True

test/test_examples_e2e.py

@@ -5,6 +5,7 @@
 import subprocess
 import sys
 import json
+import shutil
 from pathlib import Path
 
 import pytest
@@ -52,3 +53,32 @@ def test_examples_end_to_end_outputs_match_goldens(tmp_path: Path) -> None:
         assert item["run_ok"] is True
         assert item["output_match"] is True
         assert item["error"] == ""
+
+
+@pytest.mark.skipif(not has_zig(), reason="zig not installed")
+def test_examples_verifier_fails_when_golden_fixture_is_missing(tmp_path: Path) -> None:
+    examples_dir = tmp_path / "examples"
+    fixtures_dir = tmp_path / "fixtures"
+    examples_dir.mkdir()
+    fixtures_dir.mkdir()
+    shutil.copy(PROJECT_ROOT / "examples" / "001_hello.a7", examples_dir / "001_hello.a7")
+
+    result = subprocess.run(
+        [
+            sys.executable,
+            str(VERIFY_SCRIPT),
+            "--examples-dir",
+            str(examples_dir),
+            "--fixtures-dir",
+            str(fixtures_dir),
+        ],
+        cwd=PROJECT_ROOT,
+        capture_output=True,
+        text=True,
+        timeout=180,
+    )
+
+    combined = (result.stdout or "") + (result.stderr or "")
+    assert result.returncode == 1, combined
+    assert "missing golden fixture" in combined
+    assert not (fixtures_dir / "001_hello.out").exists()